1. Technical Field of the Invention
The present invention relates to a computer system, and in particular, to a file management system that uses a file system in order to manage data on a memory medium of a memory device incorporated in this computer system.
2. Related Art
In general, computers or systems with computers have memory devices to memorize data therein. The technique for managing data memorized in those memory devices is called file system and the file system is provided as one of the functions owned by an operating system (OS). Hence, each operating system uses a different file system. The file system is in charge of setting of a technique to register data, the location of a region to be managed, and how to use the region, in addition to produce folders (directories) in memory devices and files and transferring and deleting the folders.
Because the file system may conceptually include management regions defined on a memory medium and information in relation to the management, the file system will be understood in such broad manner set forth herein below. In addition, the memory device means devices including hard disks, floppy disks and CD-ROMs. In those memory devises, data is managed in blocks such that plural sectors (for example, four sectors) of data are handled as one cluster to be managed block by block. The file is referred as a gathering of data recorded in a memory device. The operating system manages such data file by file. Each file is made up of data (actual data) composing actual contents of this file and management information (file management information) used to manage the data.
When a file is deleted (removed) in the conventional file system, it is usual that file management information is solely deleted from a recording medium in a memory device, wherein practical data (i.e., actual data) of each file are left in sectors on the recording medium. This means that, until such sectors are used again on the recording medium, that is, new data are overlaid on such sectors, the original data, which have been thought by users that they are already deleted, are left as they are in the recording medium. Therefore, in cases where the memory devices such has hard disks are disposed of, there is certainly a risk that private information and/or company information are leaked from such memory devices which are thought to be disposed of.
With taking such a risk into consideration, file systems in which security for the information leakage is improved have been known as well. In those file systems, all sectors themselves in which actual data of files are stored (in the conventional common file systems, it was unnecessary to delete such actual data) are deleted by overlaying predetermined fixed data thereon. This deleting operation results in increases in the access frequency to recording mediums such as hard disk depending on how frequently the deletion operations are performed, which provides a poor access performance.